I don't think they should bring back Nightcrawler, well not yet. I just watched X2 last week and I think it would be weird to see Nightcrawler again with the X-Men especially X2 was released almost a decade ago and he didn't appear in X3. If they are gonna bring him back, it should be a proper comeback, like they should show and explain why he came back to the X-Men. I don't want FOX to bring him back just for the purpose of bringing back fan-favorites from the original trilogy.